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Earlier this year we reviewed battery safety in small electronic devices in response to media coverage of phones and e-cigarettes bursting into flames when charging. However recent news in the run up to Christmas has prompted us to return to this topic.

Hoverboards are self-stabilising scooters driven by the user shifting their centre of gravity and can reach speeds above 10mph with a range of over 20 miles. The lithium-ion batteries usually found in small portable electronics store between 10-20Wh of energy whereas these hoverboards typically store 150Wh! The media has been reporting unfortunate incidents with some of these boards, and dramatic videos have been posted of them ejecting flaming batteries as users stand by stunned. The chaos caused has closed shopping malls in the US, burnt down homes in the UK and, as a result, what could’ve been the most popular festive gift this year has been pulled from the shelves by leading retailers. Amazon’s latest message to its customers; throw unsafe hoverboards away!

In our previous blog we investigated a similar failure mode with some e-cigarettes which was causing the batteries to reach unsafe conditions. We identified this was down to poor protection of the battery by the designers when they split safety circuits between the e-cigarette and its charger. During our investigation we analysed the failure modes and conducted in-house testing, with some explosive results!

Should we be worried? Well, your smartphone contains a li-ion battery - exactly the same type as used in hoverboards – so is it going to explode? No! Phones are in daily use by the majority of the population without any issues, so what turns a proven stable technology into a primed explosive?

Press reports suggest these models are failing because of the charging circuit placing the batteries in an unsafe condition. While this is certainly possible and was the reason behind the e-cigarette failures, there may be other factors at play here. Li-ion batteries are tested thoroughly during production and it is common for surprisingly high numbers to have faults and to be rejected during factory testing. This type of testing takes time so when there is pressure to increase production – to meet Christmas deadlines for example – testing may be scaled back, and this can result in potentially dangerous batteries finding themselves assembled into products.

The lesson is simple: to ensure product safety and quality you need to carefully manage both the design and supply chain. Process failure mode and effect analysis (PFMEA) is a technique that can quickly identify these manufacturing pitfalls so that procedures and controls to mitigate them can be established and enforced.

As well as designing new products, Cambridge Design Partnership also helps companies set up and manage their supply chains. This includes identifying and selecting suppliers, reviewing and finalising the design for manufacture, developing a robust quality plan and managing the implementation of the manufacturing process and any regulatory submissions. If we can help your company with any of these challenges, please get in touch. Season’s greetings!

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